The goal of this project is to understand some of the mechanisms underlying synaptic integration in identified neurons receiving synaptic inputs from different neurons utilizing various neurotransmitters. The system we plan to study is a neural circuit in the buccal ganglia of the marine mollusc, Aplysia californica. This circuit contains several identifiable neurons which receive convergent cholinergic and serotonergic synaptic inputs as well as extensive, redundant inputs from neurons whose transmitter is not yet identified. This system permits a detailed study of heterosynaptic integration of responses involving a variety of postsynaptic potentials (excitatory, inhibitory, multi-component). This project proposes to determine whether certain transmitters or certain transmitter-induced conductances have unique effects on neural integration. Our efforts will at first be focussed on the identification of the transmitters utilized in such convergent neural circuits as described above. Systems where the transmitters utilized in the circuit are identified also permit greater insight into the mechanisms underlying neural integration and may permit a rationale for pharmacological manipulation of the system.